ES2712640T3 - Integration of a Fischer-Tropsch system and generation of synthesis gas - Google Patents

Abstract

A method of separating components, comprising: cooling a syngas stream (36) to room temperature and passing said cooled gas through a separator (38) to remove condensed water; passing the synthesis gas (39) coming out of said separator (38) to a first stage Fischer-Tropsch reactor system (40), thus obtaining a product stream (58) from said Fischer reactor system (40). First stage Tropsch at a temperature where no solid hydrocarbons are present; passing the product stream (58) through a first separator (41), thus producing a first aqueous stream (42), a first hydrocarbon stream (43) and a first gaseous product stream (44) that passes into a second stage Fischer-Tropsch reactor system (45); passing the outlet stream (46) from the second Fischer-Tropsch reactor system (45) to a second separator (47) thus producing a second aqueous stream (48), a second hydrocarbon stream (49) and a second stream ( 50) of product gaseous at room temperature; sending the first and second hydrocarbon streams (43, 44) to a treatment system (70) comprising hydrotreating and cracking, isomerization, and product separation by distillation; rubbing the second gaseous product stream (50) with a light oil (53), in an oil scrub tower (51) to remove a mixture of C3 and C4 and to produce an outlet oil stream (52) comprising the light oil (53), C3 and C4 hydrocarbons, in which the light oil (53) is taken from a product distillation system of the treatment system (70) and has no content of C3 and C4 hydrocarbons, where said system (70) treatment is fed by the first and second hydrocarbon streams (43, 44) and a stream of pure H2 (81); returning the outlet oil stream (52) to said product distillation system from said treatment system (70); thus separating C3 and C4 from the outlet oil stream (52) into two separate streams (53, 71) using the distillation columns of said product distillation system (70); divide the gas (54) that leaves the oil rubbing tower (51) into two streams, a first stream (26) to be treated in a separator (57) to obtain pure CO2 (27) and a second stream ( 55) larger containing CO2, H2, CO, CH4, unreacted and inert C2 hydrocarbons, where said second stream (55) is compressed (56) and passed to the synthesis gas generation system that provides the gas stream synthesis (36).

Description

DESCRIPTION

Integration of a Fischer-Tropsch system and synthesis gas generation

Priority claim

This application claims priority to U.S. Patent Application Serial No. 61 / 530,147, filed on

September 1, 2011.

Technical field

This invention relates to the integration of a Fischer-Tropsch (FT) system and the generation of synthesis gas.

Background

An integrated FT plant comprises a synthesis gas generation system of H ² + CO that provides feed gas to a Fischer-Tropsch catalytic hydrocarbon synthesis system with an associated system of energy and thermal energy.

High efficiency, low capital cost, together with a low carbon footprint, are the main objectives of a total installation. U.S. Patent 6,534,551 describes an integrated synthesis gas generation system comprising a two-stage synthesis gas generation unit integrated with a gas turbine that provides at least part of the energy required to drive a production plant of O ² . The O ² plant can be either a cryogenic air separation unit or a mixed O ² oxide ion transfer membrane reactor at high temperature integrated with the gas turbine. The two-stage synthesis gas generator comprises a POX or ATR coupled in any case in a parallel configuration with a catalytic gas / hydrocarbon heated reformer (GHR) in which the heating gas is the total mixed product of each reactor.

The FT hydrocarbon synthesis reactor can comprise either a single-stage or a two-stage system with cooling and separation between the phases of the aqueous and hydrocarbon liquid phases of the unreacted synthesis gas and the inert components in the gas phase . This gas stream separated from the first stage is heated and used as a feed to the second stage FT reactor. The related additional prior art is disclosed in CA 2752839 A1, US 6,958,364 B1 and US 2007/0142481 A1.

Several different designs of FT reactors are possible. The two most frequently considered are the paste bed and fixed bed bubbling bed configurations. Whatever the design concept for the FT reactor system that is adopted, there must be a procedure to efficiently use the uncondensed exhaust gas that exits the FT system so that it can be used effectively in the FT system. generation of synthesis gas. The exhaust gas contains significant flows of H ² and CO without reacting plus a large amount of CO ² , CH ⁴ C ² , C ³ and C ⁴ . C ³ and C ⁴ should be eliminated as valuable products, mostly recycled to the synthesis gas generation section together with the CH ⁴ and C ² fraction, while the inert N ² + A should be eliminated to avoid a accumulation in the system. The treatment of this exhaust gas with the maximum thermal efficiency and the minimum emission of CO ² to the atmosphere at low cost of capital and energy consumption is the object of this invention.

Summary

A method for separating components includes receiving exhaust gas from a Fischer-Tropsch hydrocarbon synthesis reaction process. The exhaust gas is rubbed with a light oil at least at a near atmospheric temperature to substantially remove a mixture of C ³ and C ⁴ . C ³ and C ⁴ are separated from the mixture in two separate streams using distillation columns in a Fischer-Tropsch. The method according to the invention is defined in claim 1.

The details of one or more embodiments of the invention are set forth in the accompanying drawings and in the description below. Other features, objects and advantages of the invention will become apparent from the description and drawings, and from the claims.

Description of the drawings

FIG. 1 is an example of a system for integrating an FT system and the synthesis gas generation.

Similar reference symbols in the various drawings indicate similar elements.

Detailed description

The exhaust gas of a Fischer-Tropsch hydrocarbon synthesis reaction process after condensation and the elimination of the aqueous and hydrocarbon liquid phases will be treated in the following sequence:

1. Rub the exhaust gas with a light oil at a temperature close to atmospheric to remove most of the C ³ and C ⁴ hydrocarbons plus traces of higher molecular weight hydrocarbons present in the gas phase. The light oil is taken from one of the product streams produced in the hydrotreating, isomerization and oil / FT wax separation unit. The light oil containing the dissolved C ³ and C ⁴ components is returned to the distillation columns in the FT improvement unit where the C ³ + C ⁴ hydrocarbons are separated and removed as product streams.

2. The exhaust gas FT retains a fairly high pressure, since typically, the feed of the synthesis gas FT is 40 bar, while the exhaust gas is about 36 bar. The exhaust gas contains the net excess of CO ² produced mainly in the synthesis gas generation unit that must be continuously removed from the plant plus the CO ² that must be recycled back to the synthesis gas generation unit to achieve required ratio of CO to H ² in the FT feed. This proportion is typically in the range of 1.9 to 2.1.

A highly efficient treatment of the exhaust gas FT after the removal of C ³ + C ⁴ is to separate a portion of the gas and eliminate substantially all the CO ² equivalent to the net excess of CO ² that occurs throughout the system. The CO ² can be removed by absorption in a rubbing system with physical or chemical solvents, such as Selexol or amine.

The separate CO ² stream is available for sequestration in a geological structure or for use in improved oil recovery operations after compression. The gas stream treated from the CO ² separation unit can be used as a part of the fuel stream for the gas turbine without any additional compression. If pure CO ² is not required, the separate portion of the exhaust gas FT containing the net product of CO ² from the entire FT installation can be used as a part of the gas turbine fuel stream and the CO content. ^{2 will} be discharged into the atmosphere with the gas turbine exhaust from the heater to fire. The remaining volume of the exhaust gas, which contains the recycled CO ² plus some (CO + H ² ) and the C ¹ + C ² hydrocarbons, is then compressed to a low pressure ratio and recycled to the gas feed point. synthesis. The compression is adiabatic without a rear refrigerator, so that the heat of the compression is retained in the pressurized recycle gas stream. The recycle gas is desulphurized before being mixed with the feeds of fresh desulfurized natural gas to POX or ATR and to g Hr.

3. The exhaust gas of the FT system that follows (C ³ + C ⁴ ) and the CO ² removal steps of the net product are compressed to the input pressure of synthesis gas generation plus the pressure drop of the system . It is then mixed with the net natural gas feed to the synthesis gas generation section to produce two separate feed streams, one for the ATR and the other for the GHR. The GHR produces approximately 27% to 30% of the synthesis gas (CO + H ² ), while the ATR produces approximately 70% to 73% of the synthesis gas. Despite this, it is beneficial to feed 40% to 60% of the recycling stream to the GHR and the remaining recycling gas to the ATR. The deviation towards the GHR is due to the difference in the reaction pathways for the CO and H ² portion of the recycling gas feed to these units. In the ATR or POX reactor, H ² and CO react with O ² and oxidize to CO ² and H ² O in the POX burner that produces heat that reduces the required natural gas feed rate by an equivalent amount. In the GHR, the CO and CO ² in the recycle stream initially experience a methanization reaction with the hydrogen that reduces the requirement for natural gas feed due to the release of heat from the reaction and the production of CH ⁴ . The net effect is more favorable in terms of the improvement of thermal efficiency in the catalytic steam / natural gas reformer GHR compared to the ATR. A separate effect is a slightly greater conversion of recycle CO ² to CO by reaction of change with hydrogen in the GHR as compared to the ATR.

4. An additional important consideration of the proposed treatment procedure is the elimination of (N ² + A) with the portion of the exhaust gas FT that contains the net product of CO ² that is defined in (2). The accumulation of N ² + A in the system as defined is approximately five times the flow of fresh A and N ² in the system from the oxygen and natural gas feed streams. Note that another point in the system where the N ² + A is removed is the hydrogen PSA that is fed with a displaced and cooled portion of the gas stream of synthesis of the product leaving the waste heat boiler. The low pressure waste gas of this PSA containing (A + N ² ) is added to the fuel gas stream that is burned in the gas turbine fire heater.

FIG. 1 shows a diagram of the process. The heat and material balance for important points in FIG1 is shown in Table 1.

Fresh natural gas feed 1 and recycled fuel gas 2 are preheated in heat exchanger 3 and desulfurized separately in units 6 and 7 of all organic and inorganic sulfur compounds. Output currents 58 and 60 are heated in passes 59 and 61 of heat exchangers. The heated streams 10 and 11 are mixed separately in the proportion of 50% of the flow of recycle stream 11 to reactor 33ATR, stream 12 and 50% of the recycle stream to reactor 34 GHR, stream 62. The total feed stream remaining to reactor 33 ATR, stream 13 comprises the stream 63 of natural gas mixed with a stream 15 of superheated steam and a stream 17 of preheated oxygen. The total feed flow to reactor 34 GHR, stream 14 comprises stream 64 of natural gas stream mixed with stream 16 of superheated steam and portion of recycle stream 62. The outflow stream 31 of the reactor 33 ATR is combined with the outflow of the open end tubes filled with catalyst in the 34 GHR reactor and the combined total flow on the shell side of the GHR tubular reactor is used to provide the heat required for the steam reforming reaction. /hydrocarbon. The total stream 32 of the synthesis gas product exiting the shell side of the reactor 34 GHR passes through a waste heat boiler 72 which generates high pressure steam 65 and a heat exchanger system comprising a set of exchangers. of heat providing heat 21 and low pressure steam 73 with condensed inlet stream 74. Part of the steam stream 73 is used for the regeneration of the amine solvent in the CO ² removal unit. The synthesis gas stream 36 cooled to a temperature close to the ambient temperature passes through a separator 38 where the condensed water 37 is removed and the gas stream 39 passes to the first stage of the Fischer-Tropsch fixed-bed catalyst in systems 40. of tube reactor including heat exchange to heat the synthesis gas to the required reaction temperature and to cool the products coming out of the reactor tubes. The total product stream 58 of the reactor system 40 at a temperature at which no solid hydrocarbons are present passes through a separator 41 which produces an aqueous stream 42, a stream 43 of hydrocarbon and a stream 44 of gaseous product passing to the second stage FT reactor system 45. The output stream of the reactor system 45, stream 46 is separated at 47 into an aqueous stream 48, a stream 49 of hydrocarbons and a stream 50 of gaseous effluent. The two aqueous streams 42 and 48 are combined and sent to a water treatment system. The two streams 43 and 49 of hydrocarbons are sent to a treatment system 70 comprising hydrotreatment and cracking, isomerization and separation of products by distillation. Each of the FT reactor systems 40 and 45 is fed on the shell side of the tubular reactors with preheated condensate streams 66 and 68 which produce steam streams 67 and 69 using the exothermic heat of the synthesis FT reaction. . The final gas product stream 50 at a temperature close to ambient temperature passes to an oil rub tower 51 where it is rubbed with a fraction 53 of light oil taken from the distillation system of the product in unit 70 and having no oil content. C ³ and C ⁴ hydrocarbons. The content of C ³ and C ⁴ of stream 50 is largely eliminated in the oil outlet stream 52 which is returned to the distillation unit of the product in which the C ³ and C ⁴ adsorbed from stream 50 are they separate and recover as part of product streams 71. The gas 54 leaving the rubbing tower 51 is divided into two streams. The first stream 26 contains all the CO ² that is produced as the net product stream throughout the facility. It is treated in the separator 57 of CO ² , which in this case is an amine system that uses part of the low pressure steam 73 for regeneration. The CO ² separator 57 can then be compressed to 72 and deliver 83 to a pipe for disposal. The second much larger current 55 that contains all the recycled CO ² plus (H2 + CO) without reacting more CH ⁴ and C ² hydrocarbons and (N ² + A) inert is compressed in 56 and passes without any type of cooling as stream 2 to the synthesis gas generation system. The treated gas stream 24 leaving the CO2 removal amine rub system 57 is mixed with a natural gas feed stream 84 to form the total fuel gas stream 23 to the gas turbine 85. The gas turbine is directly coupled and provides full power for the main air compressor 86 which delivers a feed air vapor 29 to the cryogenic oxygen plant 87. The gas turbine is also coupled to an electric generator that provides the excess energy used primarily to provide electric power for the drive motor of the air-reinforcement compressor that is part of the oxygen-pump cryogenic oxygen plant 87. The oxygen plant 87 supplies an oxygen stream 17 with a purity of 99.5 mole% to provide feed to the ATR 33 without the need for additional compression. A stream 30 of residual nitrogen is discharged into the atmosphere. A portion of the synthesis gas stream 88 leaving the waste heat boiler 72 as the stream 75 passes through a CO catalytic converter, which converts most of the CO by reaction with the excess of steam to H ² + CO ² . The outlet gas stream 89 is cooled in step 77 of the heat exchanger that produces the heat stream 78 and the stream 79 enters the multileck pressure swing adsorption unit 80. The feed stream is separated into a pure H ² stream 81 which provides the H ² required for the product improvement system 70 together with a low pressure fuel gas stream 82. The fuel gas stream 82 together with a natural gas stream 19 provides the fuel streams to a fire heater 89 which uses the hot gas turbine exhaust stream 90 as an oxidizing gas. This heater provides steam 20 of heat. The heat currents 20, 21 and 78 together provide the heat required for the preheating of the feed streams including the superheat steam and the heating of the natural gas, the recycle gas and oxygen streams. The N ² + A network that enter the system in the natural gas feed and the O ² concentrate in the plant, and are contained in the fuel gas streams 24 and 82, so that after the combustion are discharged to the atmosphere through the exhaust stream 21 from the heater 89 to fire. The high pressure steam stream 65, the medium pressure steam currents 67 and 69 and part of the low pressure steam stream 73 are superheated and used to provide power in a steam turbine system.

Several embodiments of the invention have been described. However, it will be understood that various modifications can be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.

Claims (1)

1. A method for separating components, comprising: cooling a stream (36) of synthesis gas to room temperature and passing said cooled gas through a separator (38) to remove the condensed water; passing the synthesis gas (39) leaving said separator (38) to a first stage Fischer-Tropsch reactor system (40), thereby obtaining a product stream (58) from said Fischer-reactor system (40) Tropsch of first stage at a temperature in which there are no solid hydrocarbons present; passing the product stream (58) through a first separator (41), thus producing a first aqueous stream (42), a first stream (43) of hydrocarbon and a first stream (44) of gaseous product passing to a stream. Second stage Fischer-Tropsch reactor system (45); passing the output current (46) of the second Fischer-Tropsch reactor system (45) to a second separator (47) thus producing a second aqueous stream (48), a second stream (49) of hydrocarbons and in a second stream ( 50) of gaseous product at room temperature; sending the streams (43, 44) of the first and second hydrocarbons to a treatment system (70) comprising hydrotreatment and cracking, isomerization and separation of products by distillation; rubbing the second stream (50) of gaseous product with a light oil (53), in an oil rubbing tower (51) to remove a mixture of C ³ and C ⁴ and to produce a stream (52) of oil output comprising the light oil (53), C ³ and C ⁴ hydrocarbons, in which the light oil (53) is taken from a distillation system of the product of the treatment system (70) and has no C ³ hydrocarbon content and C ⁴ , wherein said treatment system (70) is fed by the first and second hydrocarbon streams (43, 44) and a pure H ² stream (81); returning the stream (52) of output oil to said distillation system of the product of said treatment system (70); separating asf C ³ and C ⁴ from the stream (52) of output oil in two separate streams (53, 71) using the distillation columns of said product distillation system (70); dividing the gas (54) leaving the tower (51) of rubbing oil into two streams, a first stream (26) to be treated in a separator (57) to obtain pure CO ² (27) and a second stream (55) larger containing CO ² , H ² , CO, CH ⁴ , unreacted and inert C ² hydrocarbons, where said second stream (55) is compressed (56) and passed to the synthesis gas generation system which provides the stream of synthesis gas (36).